Drop-down selection cannot be made when tool-tip appears

[devmaestro1]

Reproduce steps:

1. When pulling down the drop-down tree, linger over the item so the tool-tip appears.
2. Then, try to click the item, it won't select the item. This is because the tool-tip seems to be stealing the 'MouseClick' event.

[devmaestro1]

Fixed this issue in my fork.